1. Field of the Invention
The present invention relates in general to a circuit of an electronic equipment, and particularly to a circuit which capable of saving power of a battery within the electronic equipment when the electronic equipment is switched off.
2. General Background
In recent years, as electronic equipments decrease in size and thickness, portable electronic equipment hand-carriable by users, such as, so called notebook personal computer, becomes important more and more in the market and has widely spread in today's business scenes. In those circumstances where AC power is not available, the electronic equipment typically including such notebook computers will be electrically driven by rechargeable batteries loaded therein. It will be desirable for most users that the electronic equipment runs longer before the battery runs down.
FIG. 3 illustrates a conventional power supply circuit used in notebooks. The power supply circuit includes a charger 10, a voltage regulator 12, and a power management unit 14. When an AC power source is connected to an AC adapter 11, electronic power is supplied from the AC adapter 11 to the charger 10. Then the electronic power is supplied to the voltage regulator 12, the voltage regulator 12 regulates the input voltage to 3.3V and 5V, then desired supply voltage of 3.3 or 5 V produced by the voltage regulator 12 are supplied to the internal circuit(s) of the notebook. Wherein, an output voltage of 3.3V is provided to the power management unit 14. The power management unit 14 controls the internal circuits of the notebook. When a battery 16 is used to provide the power to the notebook, the electrical power is supplied to the power management unit 14 through the charger 10 and the voltage regulator 12.
When the notebook is powered off, if the battery 16 is not drawn out from the notebook, the power management unit 14 may draw an amount of power. If the user did not use the notebook for a long time, the battery may run out of power. When the notebook run out of power during travel or out-door sport, and AC power is not available, the battery may not have enough residual energy to power the notebook, this may cause complications for the users.
What is needed is a circuit which capable of saving battery power within a notebook when the notebook is powered off.